Patent Literature 1 discloses a power semiconductor module having a semiconductor element, a collector electrode, an emitter electrode and a gate electrode junctioned to an insulating substrate with solder or the like. In this power semiconductor module, the temperatures of the semiconductor element and the component parts are measured with thermocouples, and degradation of the junction interface and the condition of cooling of a device are grasped from the measured changes in temperature. If a crack occurs and grows in the junction interface, the heat resistance increases and an increase in temperature occurs. Therefore, the progress of cracking can be determined by measuring the rate of increase in temperature.